This invention relates to processes for producing phosphazene compounds, particularly alkoxy and aryloxy substituted phosphazene compounds. Also the mercapto analog of these alkoxy and aryloxy phosphazene compounds are included. Recent interest has developed in such phosphazene compounds for use in high temperature materials, polymers and flame retardants.
In general, processes for producing alkoxy, aryloxy and mercapto-substituted phosphazene compounds are known. For example, the reaction of a halophosphazene or phosphonitrilic halide with alcohols or thiols is known and described at considerable length in Allcock, Phosphorus-Nitrogen Compounds, Academic Press, New York, 1972. According to Allcock, the reaction medium has a great influence on the reaction, affecting such variables as time of reaction, type of product produced, and purity of the product. Various solvents are known as reaction media for the substitution reactions for alcohols and thiols on phosphazene compounds. Typical of these are diethyl ether, tetrahydrofuran, dioxane, benzene, toluene, xylene, dimethylformamide, fluorocarbon-t-butylamine, pyridine and excess amounts of the alcohol or thiol used as a reagent. Unfortunately, many of these solvents provide problems in commercial processes because of emulsion formation on subsequent water-washing of the substituted phosphazene product. This causes problems in overall yield through loss of product and problems of solvent recovery which are unacceptable in commercial processes.
Also in such substitution reactions, the solvent used in the production of the phosphonitrilic halide itself may be present, which is different from the desired solvent useful in the substitution reaction. Thus, a mixed solvent system may result in the substitution reaction. This additional solvent must be removed and a further solvent removal step is required. Mixed solvent systems present difficult problems of solvent separation from product and solvent recovery. Solvents used in the production of phosphonitrilic chloride are symmetrical tetrachloroethane, monochlorobenzene, dichlorobenzene, nitrobenzene and the like. Thus, these solvents must be completely separated from the phosphonitrilic halide produced, resulting in extra process costs and capital investment, or they are used with the phosphonitrilic halide in the substitution reaction, causing difficult separation problems which also increase process costs and capital investment.
The process of the present invention uses a reaction medium which does not adversely affect yield. It does not require separation of the solvent used in preparing the starting phosphonitrilic halide. Further, the reaction medium can be easily separated from the product and other solvents. These features of the invention provide definite processing advantages for the production of phosphazene compounds.